The present invention relates to a hot forming die, particularly a superplastic forming die and a method of cleaning a hot forming die, particularly a superplastic forming die.
It is known to manufacture articles, or components, using a hot forming process, or a superplastic forming process, in which a hollow metal preform is located in a split hot forming die. The metal preform is heated to a high temperature and pressure is applied internally of the metal preform to form the metal preform into the shape of the split hot forming die.
The split hot forming die is precision cast and precision machined to produce accurately shaped surfaces for the hot forming of the articles or components. The split hot forming die is very expensive to produce and the precision of the surfaces of the split hot forming die determines the shape of the articles or components.
During the hot forming process the high temperature and the pressure applied internally of the metal preform is sufficient to cause the metal preform to become diffusion bonded to the split hot forming die. However, a stop off material, for example boron nitride, is applied to either the surface of the split hot forming die or to the surface of the preform to prevent diffusion bonding between the metal preform and the split hot forming die.
In use the stop off material builds up on the surfaces of the split hot forming die. The stop off material is removed periodically from the surfaces of the split hot forming die because the build up of stop off material gradually effects the quality of the articles, or components, manufactured. Currently the stop off material is removed from the surfaces of the split hot forming die by abrasives, for example grinding wheels, dressing stones etc.
The use of abrasives to remove the stop off material is undesirable because there is a risk that the abrasive may damage the surfaces of the split hot forming die. The damage to the split hot forming die may result in the manufacture of articles, or components, which are not in conformance with the desired shape and size. Additionally the split hot forming die may have to be re-cut to reproduce the accurately formed surfaces of the split hot forming die. Accordingly the present invention seeks to provide a novel method of cleaning a hot forming die which reduces, preferably overcomes, the above mentioned problems.
Accordingly the present invention provides a method of cleaning a hot forming die, the hot forming die having at least one forming surface and the at least one forming surface having a nickel oxide layer, the method comprising washing the hot forming die in water to remove a stop off material from the at least one forming surface of the hot forming die without removing the nickel oxide layer from the at least one forming surface.
The at least one forming surface of the hot forming die may be soaked in water.
At least one pressurised jet of water may be directed at the at least one forming surface of the hot forming die.
The hot forming die may be a superplastic forming die.
Preferably the hot forming die may comprise an alloy comprising nickel, chromium and iron. Preferably the alloy comprises 55 wt % nickel, 18 wt % chromium and the balance is iron plus incidental impurities.
The present invention seeks to provide a novel hot forming die.
Accordingly the present invention provides a hot forming die having at least one forming surface and the at least one forming surface having a nickel oxide layer.
Preferably the hot forming die is a superplastic forming die.
Preferably the hot forming die may comprise an alloy comprising nickel, chromium and iron. Preferably the alloy comprises 55 wt % nickel, 18 wt % chromium and the balance is iron plus incidental impurities.